Colouring agents are commonly used as additives in the manufacturing of food products and pharmaceuticals. A wide range of such colouring agents are commercially available making it possible, when a particular colour tone is desired, to select a single agent having the desired colour or a mixture of agents which in an appropriate combination impart the desired colour to the product.
The commercial colouring agents can be synthetic substances which are also normally referred to as dyes or azodyes, or the agents can be pigments of natural origin, e.g. in the form of plant material containing the pigment or as more or less purified pigments extracted from plants, animals or microorganisms.
Occasionally, food grade or pharmaceutically acceptable colouring agents are provided in the form of synthetic or artificial substances having the same chemical composition as naturally occurring pigments. This type of colouring agents are also referred to in the art as “nature identical” colours. However, in the present context the term “natural pigment” is used exclusively to designate pigments which are derived from a natural source.
Food grade or pharmaceutically acceptable natural pigments can be water soluble or they can be essentially water-insoluble or sparingly soluble in water, including hydrophobic pigments. A water soluble natural pigment as such can only be used for colouring a product having an aqueous phase during and/or after manufacturing. Similarly, the use of a hydrophobic natural pigment as such requires that the product to be coloured has a lipid phase in which the pigment is soluble.
Certain pigments of natural origin such as metal chelates of carminic acid and curcumin, norbixin and chlorophyllin are insoluble in water at neutral pH or below but soluble in alkaline solutions. In this context, the term “natural hydrophilic water-insoluble pigment”, refers to pigments of natural origin which are generally insoluble in aqueous media at about neutral pH or below but soluble in aqueous media at pH values in the alkaline range. Accordingly, the natural hydrophilic water-insoluble pigments which are dissolved in alkaline media precipitate at a pH level below 7.
However, it may be desirable to obtain the colour tone of a particular water-insoluble, hydrophilic natural pigment or a mixture of such pigments in a food product or a pharmaceutical product which does not comprise a phase in which the pigment is readily soluble, e.g. an aqueous phase with a pH value below 7. There is therefore an industrial need for colouring agents containing water-insoluble, hydrophilic natural pigments in the form of acid-proof water-miscible or water dispersible compositions.
Commercial water dispersible preparations of water-insoluble natural pigments such as carmine are e.g. available from Overseal Foods Ltd, Derbyshire, England under the trade name miChroma™. These products are provided as suspensions in propylene glycol and glucose syrup and the manufacturer states in data sheets that the products will stain clothing and skin.
In the pharmaceutical industry and the food industry colouring agents are used widely for the colouring of sugar coatings of e.g. sugar confectioneries, dragees, tablets, pills, gums and granulates. Presently, most colouring agents available for this purpose are based on synthetic dyes, e.g. in the form of food grade lakes which are pigments formed by precipitation and absorption of a dye on an insoluble base or substrate, such as alumina hydrate. A wide range of coating compositions comprising such lakes are available. Presently, propylene glycol-based dispersions are commonly used to incorporate such dyes into solutions used for film-coating of pharmaceutical tablets. It is recognized in the art that propylene glycol has a negative effect on both the processing time and physical properties of the film.
WO 92/11002 discloses a film-forming composition for use in coating tablets and capsules, consisting of powdered pigment particles, a film-forming, water soluble or water dispersible, edible polymer and about 1–30% by weight of water. This composition is described as a wet powder blend and it is manufactured by blending the dry ingredient followed by the addition of water by spraying it onto the blend.
A well-known problem associated with the use of water soluble or dispersible compositions of colouring agents is the tendency of such agents to migrate from one compartment of a food product or a pharmaceutical product to another where the colouring is undesired. This phenomenon is also referred to as “bleeding”.
It is therefore particularly desirable to have water soluble or dispersible natural pigment preparations which do not migrate during manufacturing or within the finished product during storage and handling, or come off when handled.
Other problems or shortages associated with known water-miscible or water dispersible natural colouring agents are low stability against light, heating, catalyst and oxygen generated changes of the colour hue and an unsatisfactory covering ability when used for coating purposes. Problems which are frequently encountered with known water dispersible compositions comprising hydrophilic, water-insoluble pigments when using such compositions in acidic media are that the pigments precipitate, separate and accumulate on surfaces and/or change their colour hue.
Thus, it is apparent that water dispersible colouring compositions containing water-insoluble, hydrophilic natural pigments, which are based on aqueous dispersions of the pigment without potentially undesirable additives including surface active substances-or propylene glycol; which are suitable for manufacturing of food products as well as pharmaceutical products, which are more stable to degradation, which do not migrate and which are not associated with the above problems have hitherto not been available to the industry.
The advantages obtained with the colouring agents of the present invention in non-powdered form include:                their use give no dusting problems as it is the case with powdered products,        in contrast to a powder product they are more readily dispersible in aqueous systems,        their manufacturing does not include a drying step which implies that the production costs are lower and that the pigments are not damaged by heat and oxygen,        they possess increased dosage performance,        they can be provided with a water content and a consistency which is adapted to the particular field of use, e.g. ranging from concentrated pastes to low viscosity products.        
In general, the advantages of the compositions according to the invention include:                they do not give rise to migration problems,        they do not contain undesirable additives,        they do not precipitate, separate and accumulate on surfaces and/or change their colour hue at low pH, i.e. they are what is referred to in the art as “acid-proof”        they make it possible to confer a desired cloudiness or reflection to otherwise clear media in a controlled manner.        